The difference between Linux kill-9 and kill-15

"My goodness! , the page editor does not have the ability to automatically save drafts. I didn't write anything yesterday. Forget it, don't care about this. I didn't write much anyway.

Hee Hee

You must be very familiar with kill-9 and often use it in your work. Especially if you're going to restart Tomcat. But for the most part, our understanding of-9 is only superficial.

Very few people (including me) take a serious look at what kill-n this n is. Criticize yourself.

All right. Let's take a good look at this familiar stranger.

1) Kill

From the help can clearly see that the-n refers to the signal number, The problem came, "signal number" is the big God???

2) kill-l (view Linux/unix's signal variable)

So much!! Say it alone today, SIGKILL and SIGTERM .

3) (kill pid), (kill-15 pid)

The system sends a sigterm signal to the corresponding program. When the program receives the signal, the following things will happen

1. The program stops immediately.
2. When the program releases the appropriate resources and then stops
3. The program may still continue to run

When most programs receive a sigterm signal, they release their resources and then stop. But there are programs that can do something else after receiving the semaphore, and these things can be

Configured. If the program is waiting for IO, it may not be done immediately.

In other words, sigterm are mostly blocked and ignored.

4) Kill -9 PID

Can't you not respond to sigterm?? Well, I will give you a kill order, I see you are not good. Most of the admin will use this command

However, not all programs will be obedient, there are always those in the state of the program can not immediately corresponding.

Appendix:

Linux Signals

Signal Name	Number	Description
SIGHUP	1	Hangup (POSIX)
SIGINT	2	Terminal Interrupt (ANSI)
Sigquit	3	Terminal Quit (POSIX)
Sigill	4	Illegal instruction (ANSI)
SIGTRAP	5	Trace Trap (POSIX)
Sigiot	6	IOT Trap (4.2 BSD)
Sigbus	7	BUS error (4.2 BSD)
SIGFPE	8	Floating point Exception (ANSI)
SIGKILL	9	Kill (CAN ' t be caught or ignored) (POSIX)
SIGUSR1	10	User defined signal 1 (POSIX)
SIGSEGV	11	Invalid Memory Segment Access (ANSI)
SIGUSR2	12	User defined Signal 2 (POSIX)
Sigpipe	13	Write on a pipe with no reader, broken pipe (POSIX)
Sigalrm	14	Alarm Clock (POSIX)
SIGTERM	15	Termination (ANSI)
Sigstkflt	16	Stack fault
SIGCHLD	17	Child process has stopped or exited, changed (POSIX)
Sigcont	18	Continue executing, if stopped (POSIX)
SIGSTOP	19	Stop executing (CAN ' t be caught or ignored) (POSIX)
Sigtstp	20	Terminal stop Signal (POSIX)
Sigttin	21st	Background process trying to read, from TTY (POSIX)
Sigttou	22	Background process trying to write, to TTY (POSIX)
Sigurg	23	Urgent condition on socket (4.2 BSD)
Sigxcpu	24	CPU limit exceeded (4.2 BSD)
Sigxfsz	25	File size limit exceeded (4.2 BSD)
Sigvtalrm	26	Virtual Alarm Clock (4.2 BSD)
Sigprof	27	Profiling Alarm Clock (4.2 BSD)
Sigwinch	28	Window size change (4.3 BSD, Sun)
SIGIO	29	I/O now possible (4.2 BSD)
Sigpwr	30	Power Failure Restart (System V)

Reference Documents :

https://major.io/2010/03/18/sigterm-vs-sigkill/
http://blog.csdn.net/ashlingr/article/details/8057825
Http://www.comptechdoc.org/os/linux/programming/linux_pgsignals.html

The difference between Linux kill-9 and kill-15